We propoe to apply the methods of biochemical genetics to the study of the systemic fungal pathogen, Cryptococcus neoformans, and in particular, to the study of the Cryptococcal capsule, a virulence factor. We shall use the newly discovered sexual phase of this organism for genetic analysis. The first steps will involve development of a stock collection of biochemical markers, such as auxotrophs and drug-resistant strains. These will next be outcrossed to the wild type, using a micromanipulator for random spore analysis. Markers which exhibit Mendelian segregation will be used for further genetic analysis, such as complementation tests and 3-point crosses. Using nutritional markers appropriately we shall attempt to perform genetic analysis by techniques easier than micromanipulation. We hope to accumulate a large number of acapsular mutants by mutagenesis and isolation of "rough" colonies. Finally, we shall classify these acapsular strains by studying the linkage of ascapsular genes to each other and to other biochemical marker genes.